68:1. There are some congregations that interrupt the blessings of the Shema in order to say Piyutim, but it is proper to avoid saying them, because they constitute an interruption in the middle of a blessing. {Rema: But some authorities rule (1) that there is no prohibition against this kind of an interruption (Rabbi Yitzchak, end of the 5th Chapter of Tractate Brachos [known as "the Ri", one of the main authorities of the Tosefos (a standard Talmudic commentary), late 12th cent.]; the Rashba [Rabbi Shlomo ben Avraham Aderet, late 13th, early 14th cent.; and the Tur [Rabbi Yaakov ben Asher, early 14th cent.]) and the practice in all communities is to say them. If one is lenient and does not say the Piyutim he has not lost anything, but he should not engage in any other matter, even words of Torah, (2) while the congregation is reciting the Piyutim, and certainly should not speak about non-Torah things. However, one is permitted to learn Torah mentally, by looking in a book and thinking, since thought is not like speech. Nevertheless, (3) as a result of one doing this others will come to speak and interrupt their blessing. Therefore, (4) one should not separate oneself (5) from the congregation in a place where the practice is to say Piyutim, (6) and one should say them together with the congregation. See below in Siman 90, Par. 10. (Maharil [Rabbi Yaakov HaLevi Molin, late 14th - early 15th cent.] and Darkei Moshe [commentary on the Tur by Rabbi Moshe Isserles, the "Rema", who is also the author of this commentary on the Shulchan Aruch (i.e., he's referencing another work of his), mid 18th cent.])}